How do you adjust the clutch on a Class 7 or 8 truck?

Answer 1

Assuming you have an Eaton-Fuller twin countershaft transmission, you need to get under the truck and remove the access plate (if it's still there). I don't remember offhand the socket size for that, but I do believe it's ASE (with the fleet for the company I work for, most trucks don't have the access plate).

The adjustment bolt.. you'll see it.. it's the only five sided bolt on the pressure plate, and it'll be between two round rivets. If you don't see it right away, you'll have to bump the starter (or have a buddy do it for you while you observe to see when it's positioned right). Once it's in position, then you have to depress the clutch.. if you have someone to do it, they can depress it... I usually use Blue Point hood prop rod for this (Harbor Freight, O'Reilly Auto Parts, Auto Zone, Advanced Auto Parts, Pep Boys.. they all sell something similar.. it's just a telescoping rod which you can lock into position).. adjusting the clutch, you need a 5/8" socket.. you can use a 3/8" or 1/2" drive ratchet for this... doesn't really matter, so long as you can reach.. I usually use my 1/2" drive, because it has a longer handle, and my 3/8" sockets have the button on the back to release the socket, and they get in the way... you get the ratchet onto that bolt, then you take a prybar and push on the back of the socket.. once the bolt pushes inward, you can adjust the clutch.. clockwise (marked as "on" with some ratchet brands) increases your pedal free play.. counterclockwise (marked as "off" on some ratchet brands) decreases pedal free play. At the end of it, you should have at least 1-1/2" of free play in the clutch pedal, and a 1/2" gap behind the throwout bearing.. if you have the 1/2" gap behind the throwout bearing and you either have less than 1-1/2" or more than 2-1/2" of free play in the clutch, then you'll need to adjust the linkage.

This is universal for all Eaton-Fuller twin-countershaft transmissions, whether it's a synch box or an unsynchronized transmission. And the same holds true whether it's a linkage clutch or whether it has a hydraulic clutch (e.g., Volvos, the Kenworth T680, etc.). In the case of the hydraulic clutches, the pedal free play is self-adjusting, although you'll still have to ensure that you have the 1/2" gap behind the throwout bearing (which, by the way, you can measure with a 1/2" socket extension... no need to buy the measuring forks).

Rockwell transmissions should be more the same, although the socket sizes might vary with those.